This invention relates to the field of metalworking lubricants in general and, in one particular respect, to forging lubricants. More particularly, it relates in one aspect to a new forging lubricant composition and a method of using that composition in the hot forging of metal workpieces. Metal parts of a multitude of sizes and shapes are manufactured by various types of forging operations, and these parts are formed from stock composed of a great many metals and metal alloys. A great many parts are forged from such metals and metal alloys as, for example, steel, aluminum, titanium, and high nickel alloys, to name but a few.
The conditions under which metal parts are forged, of course, are widely variable, depending upon not only the nature of the metal, but upon the size and complexity of configuration of the desired part. Small, thin, simply shaped parts may obviously be forged from a relatively flowable metal such as aluminum under much less rigorous conditions than are required to forge large more complex shaped parts from a metal such as steel.
Each set of forging conditions requires a specialized lubricant, and there is therefore a multitude of aqueous-based, oil-based and organic solvent-based lubricants currently in use in various forging operations. Many such lubricant systems, particularly those used under the most demanding forging conditions, by their nature require the user to make compromises in order to achieve the desired functional characteristics while avoiding as much as possible any safety, occupational health or environmental hazards involved in their use. Moreover, in some instances, more restrictive health and environmental guidelines are now in force which may make the use of certain lubricant systems either extremely expensive or simply unworkable. It is to these and related concerns which the present invention is directed.
In a typical high performance forging operation, such as one which might be devoted to the manufacture of large, complex parts from aluminum alloy stock, an effective lubricant is one which ordinarily contains a variety of lubricity agents in a carrier comprising mineral oil and/or volatile organic solvents. The dies used in such forging operations are maintained at high temperatures, in the range of 350.degree. F. to 825.degree. F. in order to permit proper metal flow during the forging operation.
The forging lubricant is typically applied to the die and the workpiece by spraying, and, on account of the temperatures involved, the mineral oil and volatile organic compounds immediately flash off, leaving only a relatively small amount of residue which actually functions as the lubricant. As anyone who has observed such a forge operation well knows, the flashing off of the mineral oil and volatile organic compounds creates a significant amount of open flames, and the spray wand by which the lubricant is applied takes on the appearance of a flame thrower. Moreover, a large amount of smoke is typically generated when the mineral oil and volatile organic compounds flash off, since, at the same time, a rather significant portion of the lubricity agents may burn off as well. In this context, it is well known that any improvements in the performance of the forge lubricant which are achieved by reformulation frequently come at the cost of significantly higher smoke generation.
Similar difficulties are inherent when oil-based paste type lubricants are utilized. While the paste lubricants contain little or no volatile organic compounds, their oil carriers partially or completely burn at typical forging temperatures, resulting in significant heavy smoke generation.
The hazards, expense and environmental problems associated with such forging operations are of great proportion and are quickly becoming even more so.
In a state such as California, where environmental protection statues and regulations impose rigid standards on industrial operations, and in other states which have similar environmental protection schemes, the smoke generated by a large forge operation creates tremendous difficulties.
Since environmental agencies frequently monitor smoke emissions by aerial surveillance, there is close attention paid to reducing the smoke generated in the forging operation. Unfortunately, this often limits the efforts made to vent the smoke from the buildings in which the forge operation is housed. The result of this is a significant degradation of the air quality within the buildings.
An important economic consideration is that in California, for example, a tax may be levied upon each gallon of volatile organic compounds emitted into the air. More importantly, as air quality standards are progressively raised, there will soon come a time when a forge operation will simply be prohibited from emitting large amounts of smoke. The choice then will be to find an alternative lubricant which produces significantly reduced amounts of smoke or to cease operations entirely.
Similar problems exist with respect to the use of oil or solvent-based lubricants in smaller scale forge and other metalworking operations, since waste lubricant materials of this type are considered an environmental hazard. Disposal is therefore tightly controlled and increasingly expensive.
Other related concerns create a strong demand for alternative metalworking lubricants.
As described above, open flame is generated when conventional mineral oil and volatile organic compound-based lubricants are applied to a heated die. One must therefore have available fire prevention and fire control equipment, such as fire extinguishers and sprinkler systems, in the immediate area of the forge operation. Indeed, fire extinguishers see regular use in many forge operations, and the cost of their maintenance is significant. In general, fire prevention, fire control and fire detection systems of all types are regular and significant capital and maintenance cost items for hot forge operations.
A related problem associated with the use of conventional volatile organic compound-based lubricants is the need for special storage facilities on account of their high flammability. This too imposes a significant cost associated with the use of conventional lubricants.
Transportation of these flammable lubricants in special containers and special vehicles is yet another source of additional cost, hazard, and inconvenience associated with their use.
A still further disadvantage of conventional lubricant systems which results from the flashing off of oil and solvent carriers is that the smoke generated forms tar-like deposits on machinery, finished parts, floors, windows, and nearly everything else housed in the same building with the forge operation. Quite apart from the aesthetic undesirability of such deposits, there are economic and health concerns as well. Many large forge operations maintain permanent steam-cleaning facilities at a significant cost.
Various types of dry lubricants and methods for applying them to metal surfaces have been proposed for use in diverse environments, but none has been widely adopted on account of certain inherent disadvantages in either the lubricant itself or the method of its application.
For example, in titanium forging operations, it has been proposed to utilize a powdered lubricant composed of glass and ceramic components, with the optional use of steel shot, in a process in which the lubricant is imbedded in the forge tool surface by a high pressure spray. This process is described in terms of sandblasting the lubricant onto the tool surface, and is intended to effect a cold working and smoothing of the tool surface. Of course, such a high pressure spray process involves the use of rather expensive spray equipment, and it also presents the risk of worker injury due to misdirected spray.
Others have proposed to spray dry reactant materials onto hot metal surfaces in order to form a reaction product lubricant in situ. Still others have proposed various combinations of dry lubricant components for use in a wide range of applications. Many of these lubricant compositions, however, have drawbacks, as well.
After forging, whether with a conventional or dry lubricant, aluminum parts are subjected to a caustic etch for the purpose of removing lubricant residues. In a preferred procedure which is well known in the art, the caustic etch may be used in combination with an acid wash. In many aluminum forge operations, the acid wash advantageously precedes the caustic etch.
As is well known in the art, the conditions of these wash and etch procedures are quite harsh. Typically, the caustic etch bath is 5% to 15% by weight alkali metal hydroxide in water. Typical acid baths are similarly strong, often containing a high concentration of nitric acid. In forge operations using conventional solvent or oil based lubricants, the wash and etch procedure works quite well to remove essentially all lubricant residues from the forged parts.
Notwithstanding the harsh conditions of the wash and etch, however, it has been found that residues of powdered lubricants may still adhere to the parts with such tenacity that even subjecting the parts to physical removal procedures, such as brushing and scraping, after the etch will not adequately clean them.
It has also been found, in working with multi-component powdered lubricants, that obtaining a consistent spray pattern using conventional powder coating equipment is extremely difficult. Overspray, underspray, puffing, and sputtering have been found to be serious drawbacks, both from the standpoint of obtaining a functional lubricant coating on the workpiece and from the standpoint of efficient use of powder lubricant material. Overall, the spray process has heretofore been found too erratic to be acceptable commercially. Moreover, it has been unexpectedly found that the spray was particularly unpredictable when utilizing powder coating equipment which, as is quite common, utilizes a fluidized bed as a reservoir from which the powder was sprayed. Even utilizing powder coating equipment which has a gravity-fed reservoir has typically provided only a marginal improvement in consistency.
While the particular problems encountered in an aluminum forge operation have been described in detail, many of the same and other related concerns exist in other metal working environments. These include not only other hot forge operations, such as the manufacture of forged steel and titanium parts, but also a wide variety of other metalworking and metal forming operations. Examples include extrusion, drawing, stamping, and other hot and cold forming operations, many of which employ lubricants in aqueous or solvent based carriers. Thus, many of the same technical and economic benefits could be realized in such operations by adopting an improved dry lubricant composition.
It is therefore a principal object of the present invention to provide a forge lubricant and a method of its use which significantly reduce the amount of smoke and oily waste generated during the forging operation.
A related object is to eliminate the organic carrier materials which are essential parts of conventional high performance forging lubricants. Thus, a general object of the present invention to provide a lubricant which eliminates many health, environmental and safety drawbacks of conventional lubricants having mineral oil and volatile organic compounds as carriers.
Another more particular object is to eliminate the need for special transportation and storage facilities which are required for conventional lubricants.
A further important object of the present invention is to provide a powdered lubricant composition which may be applied to a workpiece and/or die in a substantially uniform coating by the use of conventional powder coating equipment.
A related object is to provide a method of manufacturing a powdered lubricant composition which may be more readily applied to a workpiece and/or die in a substantially uniform coating by the use of conventional powder coating equipment.
Yet another important object is to provide a high performance dry lubricant which does not form residues which resist removal by conventional cleaning procedures.
Other objects and advantages of the present invention will be apparent to those skilled in the art from the following description of the invention and the appended claims.